A SIMPLE INTRA-OPERATIVE TECHNIQUE FOR ESTIMATING FEMORAL OFFSET IN TOTAL HIP ARTHROPLASTY

Surgeons are becoming increasingly aware of the importance of matching a patient’s native offset during hip arthroplasty. During the course of a previous study investigating proximal femoral geometry in New Zea-landers it was noted that accurately measuring the femoral offset of a hip arthroplasty patient by traditional methods is difficult and inaccurate. The relationship of various surface parameters were studied to find a simple and reliable method for the surgeon. Eighteen cadaver femora were skeletalised and the offset was measured using a standardised radiological technique. The femoral neck was then sectioned from a point 1–2 cm above the lesser trochanter to the base of the trochanteric fossa. The femoral head was sectioned in the coronal plane and the centre of the head located with concentric circles. The distance from the centre of the head to the most lateral spike of bone was measured. This measure was compared to the radiological offset. Offset correlated closely with the measurement from the centre of rotation to the most lateral spike of bone provided the neck cut extends to the base of the tro-chanteric fossa. Eleven of eighteen measurements were within 2mm of true offset and fifteen were within 3mm. A simple intra-operative technique taking no longer than one or two minutes and requiring no special equipment has been devised to allow the surgeon to accurately estimate the patients femoral offset.